Maybe you noticed that the ending of Mean Girls isn't like the seventy-five minutes that come before it. The film's chugging along as a snarky, Juvenalian satire of teenage girlhood, and then wham! Cady's giving an earnest speech about why it's cool to be yourself at the Spring Fling.
Wait, what? And what is a Juvenalian?
Juvenalian satire is a type of comedy that points out how messed up contemporary society is by using scathing humor and taking the moral high ground. In Mean Girls, Cady is an instrument of Juvenalian satire. After a dozen years in Africa, she enrolls at North Shore High School socially pure. She's levelheaded, smart, and uncorrupted by the materialism and thirst for popularity of her classmates. That allows her moral superiority over them.
Then she meets Regina. Cady's descent into "Girl World" is filled with biting humor that critiques the insanity of what it's like to be a high school girl, and especially what it takes to be a popular high school girl.
The end of Mean Girls breaks from this satirical approach and skews surprisingly traditional. For starters, it takes place at a dance, like roughly 4,328 high school comedies before it. The tone changes, too. Mean Girls drops its caustic sarcasm and Cady gives a speech that's designed to bring the feels. Ultimately, the film's conventional ending doesn't erase all the delicious satire that came before, but it does seem like the end of a different flick.